JPH0539197U - AC motor controller - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] Even when the primary current command of the AC motor changes in a wide range of frequency, the gain of the current control amplifier is kept almost constant, and appropriate and stable current control is performed. A current detector for a current flowing through an AC motor, a current control amplifier 8A for inputting a deviation signal from a current command signal for commanding the current, and an AC motor for controlling current by an output signal of the current control amplifier 8A. In the control device, the current control amplifier 8A includes an operational amplifier and its input resistance Ri.
And a high-speed switching element SW having a proportional-integral circuit formed by a feedback circuit including a resistor Rf and capacitors Cf ₁ and Cf ₂ connected in series, and being connected in series to the capacitor Cf _1.
And the resistor R ₁ were connected in parallel. When the primary current command changes in frequency, the primary frequency element of the AC motor is given to the high-speed switching element SW connected in parallel with the capacitor Cf ₁ in the proportional-integral circuit, and the capacitor capacity is changed according to the primary frequency. The gain of the amplifier can be kept almost constant.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a control device for an AC electric motor.

[0002]

[Prior Art]

 FIG. 3 shows a circuit diagram of a conventional control device that controls the speed of an AC motor. In the figure, 1 is an AC power supply, 2 is a rectifier circuit, 3 is a PWM (pulse width modulation) inverter, 4 is an AC motor, 5 is a speed sensor, 6 is a current detector, 7 is a speed control unit, and 8 is A current control amplifier, 9 is a triangular wave oscillator, and 10 is a PWM circuit.

In the above control device, the speed signal ωr from the speed sensor 5 is input to the speed control unit 7 in response to the speed command ωr *, and the speed of the AC motor (IM) 4 is controlled. The speed control unit 7 calculates the speed element and the current element, and as a result, outputs the primary current command I ₁ * (AC signal) of the AC motor 4. Here, since the speed controller 7 is not directly related to the present invention, its detailed description is omitted.

The above-mentioned primary current command I ₁ * of the AC motor 4 is a deviation signal from the AC current detection signal I ₁ detected by the current detector 6 provided between the inverter 3 and the AC motor 4 The deviation signal is input to the control amplifier (ACR) 8 and proportionally integrated by the current control amplifier 8. The output signal E ₁ * of the current control amplifier 8 is PWM-modulated (pulse width modulation) by the PWM circuit 10 by the triangular wave carrier output from the triangular wave oscillator (OSC) 9 and is given to the inverter 3 as a base signal. Are configured.

[0005]

[Problems to be solved by the device]

FIG. 4 shows a circuit configuration of the current control amplifier 8 in the case of configuring such a current control system. In the figure, the current control amplifier 8 is connected to the operational amplifier Amp, its input resistance Ri, a proportional multiplication circuit by a feedback circuit consisting of a series connection of a capacitor Cf and a resistance Rf, and the output of the operational amplifier Amp for feedback. It is composed of a variable resistor VR that changes the gain of the circuit. As described above, the deviation signal between the alternating current command I ₁ * and the alternating current detection signal I ₁ detected by the current detector 6 is input to the current control amplifier 8, and the deviation signal is proportionally integrated. ..

By the way, when the current flowing through the AC motor is controlled by the current control amplifier 8 and the speed is controlled, the gain of the feedback circuit is set to 1 point by the variable resistor VR. The current control amplifier 8 operates only with a constant gain in response to the AC primary current command I ₁ * in which the frequency output from the control unit 7 is variable. As a result, when the gain of the current control amplifier 8 is set to a stable current control gain at a low frequency by the variable resistor VR, the gain of the current control amplifier 8 is decreased at a high frequency, so that the primary current command I ₁ * Will not flow and stable current control will not be possible, causing problems such as vibration due to torque ripple in the output load of the AC motor and abnormal heat generation of the AC motor. Further, if the gain of the current control amplifier 8 is set to a stable current control gain at a high frequency by the variable resistor VR, the current control system becomes unstable due to the high gain of the current control amplifier 8 at a low frequency, As a result, problems such as unstable speed control occur. Such a problem becomes prominent when the AC motor is controlled over a wide range up to a high frequency above the commercial frequency.

The present invention has been made to solve the above problems, and an object thereof is to keep the gain of the current control amplifier substantially constant even when the primary current command of the AC motor changes in a wide range of frequency, and to maintain the gain appropriately. Moreover, it is to provide an AC motor control device capable of stable current control.

[0008]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention provides a deviation signal between a current detector that detects an alternating current flowing through an AC motor and an output signal of the current detector and a current command signal that commands a current flowing through the AC motor. In a control device for an AC motor, which is configured to control an alternating current flowing through the AC motor by an input current control amplifier and an output signal of the current control amplifier, the current control amplifier includes an operational amplifier and an input resistance thereof. A high-speed switching device and a resistor connected in series are connected in parallel to the capacitor, and the capacitor has a proportional-integral circuit made up of a resistor and a capacitor connected in series.

[0009]

[Action]

 In the present invention, when the primary current command changes in frequency, the primary frequency element of the AC motor is applied to the high-speed switching element connected in parallel with the capacitor in the proportional-plus-integration circuit, and the high-speed switching element is operated according to the primary frequency. Since the capacitor capacity is variable, the gain of the current control amplifier can be kept almost constant.

[0010]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a current control amplifier according to an embodiment of the present invention. Elements having the same functions as those of the configuration shown in FIG.

In FIG. 1, in the configuration of the current control amplifier 8A, an operational amplifier Amp, an input resistor Ri, a feedback circuit including a series connection of a capacitor Cf ₁ , a capacitor Cf ₂ and a resistor Rf, and an output of the operational amplifier Amp. The connected variable resistor VR is similar to the conventional current control amplifier. SW is a high-speed switching element connected in series with the resistor R _1, and is connected in parallel with the capacitor Cf ₁ . The gate signal of the high-speed switching element SW is supplied from the gate control circuit 20 that inputs the rotation frequency ωr, which is the primary frequency element of the AC motor, and controls whether the high-speed switching element SW is fully on, fully off, or on-duty controlled. To be done. Further, the deviation signal between the AC current command I ₁ * and the AC current detection signal I ₁ detected by the current detector 6 is input to the current control amplifier 8A, and the deviation signal is proportionally integrated. The output signal E ₁ * of the current control amplifier 8A is PWM-modulated (pulse width modulated) by the PWM circuit 10 by the triangular wave carrier output from the triangular wave oscillator (OSC) 9 and given to the inverter 3 as a base signal. Constitutes a current control system.

Hereinafter, the present embodiment will be described with respect to current control per phase. First, the capacitance of the capacitor as a conventional Cf = Cf ₁ = Cf _2, sets the gain of the current control amplifier 8A to a stable position at a low frequency by the variable resistor VR. At this time, the gate control circuit 20 is configured to output a signal for turning on all the high speed switching elements SW. Therefore, in the feedback circuit of the current control amplifier 8A, all the high-speed switching elements SW are turned on and the resistor R ₁ is connected in parallel to the capacitor Cf _1. However, if the resistance value of the resistor R ₁ is made small, it is almost the same as before. Is equivalent to When the transfer function G (s) of the current control amplifier 8A in this case is obtained, the following equation (1) is obtained. G (s) = (1 + Rf · Cf ₂ · s) / (β · Ri · Cf ₂ · s) ... (1) s: Laplace operator β: Gain by variable resistor (β = 0 to 1) Since the resistance value of the variable resistor is sufficiently smaller than the impedance of the feedback circuit, it is ignored.

Next, when the primary frequency of the AC motor becomes high, the gate control circuit 20 controls the high-speed switching element SW so that it is completely turned off. Therefore, in the feedback circuit of the current control amplifier 8A, the capacitors Cf ₁ and Cf ₂ and the resistor Rf are connected in series. When the transfer function of the current control amplifier 8A in this case is obtained, the following equation (2) is obtained. G (s) = (1 + Rf · 1/2 · Cf ₂ · s) / (β · Ri · 1/2 · Cf ₂ · s) (2) s: Laplace operator β: Gain by variable resistor ( β = 0 to 1) The capacitor capacity is Cf ₁ = Cf ₂ , and since it is connected in series, it is set to 1/2 · Cf _{2 in the} equation (2).

Therefore, by comparing the equations (2) and (1), it is found that the equation (2) has a time constant of 1/2 of the first-order advance element and a double gain. .. Therefore, it is possible to change the gain of the current control amplifier 8A by turning on and off the high speed switching element SW by the output signal of the gate control circuit 20. The output characteristic of the gate control circuit 20 in the case of the above control is shown in FIG. In the figure, the switching of the high speed switching element SW has a hysteresis width with respect to the change of the primary frequency f ₁ .

Next, in the case where the current control accuracy is required more than in the case of the above control of the present invention, or when the torque fluctuation of the output load of the AC motor due to the shock at the moment when the high speed switching element SW is switched becomes a problem. Another corresponding embodiment will be described.

The configuration of the current control amplifier 8A is the same as that of FIG. 1, except that the output signal of the gate control circuit 20 is turned on when the high-speed switching device SW is turned on and off as well as when it is turned on. That is, the duty control is performed. The output characteristic of the gate control circuit 20 in this case is shown in FIG. As an example of performing on-duty control, the frequency of the triangular wave that is the carrier wave is increased to several tens of KHz, and the method of comparing the speed element with the triangular wave is used. Here, simply connected in parallel high-speed switching element SW to capacitor Cf _1, the voltage waveforms across the capacitor Cf ₁ is subdirectory differential pulse by the time constant of the fast Control button on resistors and capacitors Cf ₁ Ji element SW However, the on-duty control cannot be continuously controlled. Therefore, the resistor R ₁ is connected in series with the high-speed switch element SW to increase the time constant with the capacitor Cf ₁ so that continuous control is performed. The value of the resistor R ₁ can be reduced by increasing the frequency of the triangular wave. In this way, by performing the on-duty control by the high-speed switching element SW, the capacitance of the capacitor Cf ₁ is continuously changed, and the gain of the current control amplifier is instantaneously changed from the equation (1) to the equation (2). It does not change to, but changes continuously from equation (1) to equation (2). Therefore, when the gate control circuit 20 determines the primary frequency at which the high-speed switching element SW is all on, on-duty controlled, and all off, the above-mentioned problems are solved.

[0017]

[Effect of the device]

 As described above, according to the present invention, even when the primary current command of the AC motor varies over a wide range, the primary frequency element of the AC motor is connected to the high speed switching element in parallel with the capacitor in the proportional-integral circuit. By giving it, the capacitance of the capacitor can be varied by the high-speed switch element, and the gain of the current control amplifier can be kept almost constant, so that there is an excellent effect that appropriate and stable current control can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current control amplifier according to an embodiment of the present invention.

2 (a) is an output characteristic diagram of a gate control circuit for controlling a high speed switching element in the current control amplifier of FIG. 1, and FIG. 2 (b) is a high speed switch in the current control amplifier of FIG. FIG. 5 is an output characteristic diagram of the gate control circuit when the element is on-duty controlled.

FIG. 3 is a circuit diagram of a conventional AC motor control device.

FIG. 4 is a circuit diagram of the current control amplifier of FIG.

[Explanation of symbols]

1 ... AC power supply, 2 ... rectifier circuit, 3 ... PWM inverter,
4 ... AC electric motor, 5 ... Speed sensor, 6 ... Current detector,
7 ... Speed control section, 8, 8A ... Current control amplifier, 9 ... Triangular wave oscillator, 10 ... PWM circuit, 20 ... Gate control circuit,
SW ... High-speed switch element.

Claims (1)

[Scope of utility model registration request] 1. A current detector for detecting an alternating current flowing through an alternating current motor, and a current control amplifier for inputting a deviation signal between an output signal of the current detector and a current command signal for instructing a current flowing through the alternating current motor. In an AC motor control device configured to control an AC current flowing through the AC motor by an output signal of the current control amplifier, the current control amplifier includes an operational amplifier, an input resistance thereof, and a resistor and a capacitor in series. A control device for an AC electric motor, which has a proportional-integral circuit with a connected feedback circuit, and a high-speed switching element and a resistor connected in series to the capacitor are connected in parallel.